Refrigerating apparatuses that performs a refrigeration cycle has been conventionally known and are widely used as coolers for refrigerators for storing food. For example, Japanese Patent Application Laid Open Publication No. 2002-228297 discloses a refrigerating apparatus provided with a plurality of heat exchangers for cooling the inside of a refrigerator. In this refrigerating apparatus, a refrigerator heat exchanger for cooling the inside of the refrigerator and a freezer heat exchanger for cooling the inside of a freezer are connected in parallel to one outdoor unit. Besides a main compressor of the outdoor unit, the sub compressor is provided between the freezer heat exchanger and the outdoor unit in the refrigerating apparatus. In the refrigerating apparatus, a single-stage refrigeration cycle using the refrigerator heat exchanger as an evaporator and a two-stage compression refrigeration cycle using the freezer heat exchanger as an evaporator and the sub compressor as a lower-stage compressor are performed in one refrigerant circuit.
In the above refrigerating apparatus, the evaporation temperature of the refrigerant is comparatively set low in the freezer heat exchanger connected in series with the sub compressor. Accordingly, frosting is a severe problem in this freezer heat exchanger. In detail, moisture in air attaches to the freezer heat exchanger, so that the freezer heat exchanger is frosted, which inhibits the cooling of air inside the freezer. Therefore, it is necessary to melt the frost attaching to the freezer heat exchanger, namely, to defrost the freezer heat exchanger.
For defrosting the freezer heat exchanger, an electric heater is used generally, as disclosed in Japanese Patent Application Laid Open Publication No. 09-324978. In detail, in general refrigerating apparatuses, defrosting operation is performed in a manner that air heated by electric heaters is supplied to the freezer heat exchangers to warm the air to melt frost attaching to the freezer heat exchangers by the heated air.
Or, so-called hot gas bypasses may be employed for defrosting the freezer heat exchangers, as disclosed in Japanese Patent Application Laid Open Publication No. 2001-183037. In detail, the gazette proposes that the refrigerant circulates only between the compressor and the freezer heat exchanger and the gas refrigerant of a comparatively high temperature discharged from the compressor is introduced into the freezer heat exchanger to melt frost.
Problems that the Invention is to Solve
As described above, the above refrigerating apparatuses generally use the electric heaters for defrosting the freezer heat exchangers. In this case, however, the air heated by the electric heater is supplied to the freezer heat exchanger for melting frost, which may leads to the heated air flowing into the inside of the freezer to increase the temperature inside the freezer. Further, frost attaching to the freezer heat exchanger has to be warmed from the outside by air and it takes a long period of time to defrost the freezer heat exchanger (40 minutes, for example).
The above problems have been solved to some extent by defrosting the freezer heat exchanger by the hot gas bypass. In the defrosting by the hot gas bypass, high temperature refrigerant is introduced into the heat transfer tube of the freezer heat exchanger to warm frost attaching to the freezer heat exchanger from the inside. Therefore, temperature increase in the inside of the freezer during the defrosting of the freezer heat exchanger is suppressed, in comparison with that in the case of defrosting by the electric heater.
However, during the defrosting by the hot gas bypass, the refrigerant only circulates between the compressor and the freezer heat exchanger and only heat that the compressor provides to the refrigerant can be utilize for melting frost. For this reason, a long period of time is still required for defrosting the freezer heat exchanger.
In addition, the refrigerant supplied to the freezer heat exchanger is sucked merely into the compressor again and is not utilized other than for defrosting the freezer heat exchanger. In other words, the compressor is driven only for defrosting the freezer heat exchanger during the defrosting of the freezer heat exchanger. Therefore, as in the case using the electric heater, power consumption is increased in association with the defrosting of the freezer heat exchanger, with a result of increase in running cost of the refrigerating apparatus.
The present invention has been made in view of the above problems and has its object of reducing, in a refrigerator provided with a plurality of heat exchangers for cooling the inside of a refrigerator and the like, a time required for defrosting heat exchangers for cooling the inside and reducing power consumption of the refrigerating apparatus, and in its turn, for reducing the running cost.